High-speed rail transit contact wire requires high strength, high electrical conductivity, and high wear resistance. At the same time, the manufacturing process should be successive, so that there are very few joints inside the wire. Continuous extrusion possesses the unique advantage of continuously producing wires, while the comprehensive properties of the product need to be regulated by optimizing the processing parameters. This study investigates the effects of extrusion pass on the enhancement of mechanical and electrical properties of a Cu-0.8Cr-0.075Zr alloy. The results showed that the tensile strength, elongation, and electrical conductivity of the material after three extrusion passes achieve 488 MPa, 16.6 %, and 86.8 % IACS, respectively, exhibiting the optimal comprehensive properties. At the peak aging state, the mechanical strengths show negligible decreases, while the fracture elongation and electrical conductivity were increased to 18.8 % and 88.7 % IACS, respectively. In addition, the alloy holds a high wear resistance, which largely depends on both the strength and plasticity. This research thus provides valuable insights into manufacturing high-performance Cu-Cr-Zr contact wires.

In this paper, the thermal deformation behavior of two Cu-Cr-Zr alloys with different chemical compositions, i.e., Cu-1.15Cr-0.12Zr and Cu-1.7Cr-0.2Zr alloys, was investigated at different temperatures and strain rates. The results indicated that the Cu-1.7Cr-0.2Zr alloy exhibits lower flow stresses at the same test conditions, although it has higher element contents. The diffusion activation energies were then calculated, which are 602.6 kJ/mol and 628.1 kJ/mol for Cu-1.15Cr-0.12Zr and Cu-1.7Cr-0.2Zr, respectively, suggesting that the activation energy is not the dominant reason for the lowered flow stress. TEM and EBSD characterizations revealed that the particle-stimulated nucleation (PSN) mechanism is responsible for the softening behavior. At grain boundaries, the so-called necklace structure was formed, as evidenced by optical microstructures. The true stress-strain curves show that the flow stresses at 500 degrees C similar to 600 degrees C exhibit maximum values, which are even higher than those obtained at 400 degrees C. The reason for that can be attributed to dynamically precipitated particles, which harden the alloy at these medium temperatures. The processing maps of the two alloys were then plotted, which, together with the experimental findings, can guide the production of Cu-Cr-Zr alloys in practice.

The mechanical and electrical properties of continuous extruded Cu-Ni-Si alloys can be significantly enhanced by employing a pre-aging treatment before rolling and aging processes. At the optimized pre-aging treatment, the tensile strength and electrical conductivity of the alloy can achieve 782 MPa and 48.2% IACS, respectively, showing an excellent combination of mechanical and electrical properties. The mechanisms were revealed by implementing the pre-aging treatment at different temperatures. At low pre-aging temperatures, massive dislocations can remain while only a small number of precipitates can be introduced. During the following rolling and aging processes, the nucleation of precipitates can be promoted by the retained dislocations while the total number of the precipitates is still in a relatively low volume fraction, resulting in only enhanced mechanical properties. In contrast, pre-aging at high temperatures leads to an enhanced electrical conductivity yet a lower mechanical property due to the fast nucleation and coarsening of precipitates. At medium pre-aging temperatures, the mechanical and electrical properties can be both enhanced by lowering the initial dislocation density and simultaneously boosting the nucleation of precipitates. The former facilitates the nucleation of the precipitates without coarsening, and the latter, together with the tertiary precipitates, contributes to high electrical conductivity. Thus, the results provide valuable insights into manufacturing high-performance Cu-Ni-Si alloys.

In the study, a 1.5 % TiB2 nanoparticle containing AlMgScZr composites was fabricated by the powder bed fused-laser beam (PBF-LB) at different scanning speeds, where near-fully dense, crack-free high-strength samples were obtained at a scanning speed of 500 mm/s. Systematic tensile testing reveals quasi-isotropic tensile properties: uniform elongation values are comparable between horizontal and building directions, while tensile strength differential remains 2 %. Microstructure characterization revealed that the printed samples exhibit columnar/equiaxed bimodal grain structures. The TiB2 particles in the matrix serve as nucleation sites engulfed by solidification fronts, enabling grain refinement. TiB2 further promotes the precipitation and thus increases the volume fraction of the Al3Sc and Al3Zr phase during PBF-LB fabrication. These Al3Sc and Al3Zr precipitates further promote the nucleation of fine equiaxed grains. Consequently, equiaxed grains obstruct columnar grain epitaxial growth, suppressing fiber texture development. The bimodal grain structure of weakly textured columnar grains and randomly oriented equiaxed grains contributes to the overall weak fiber texture and thus quasi-isotropic tensile properties of TiB2/AlMgScZr.

In this study, the combination of continuous extrusion and rolling process was proposed to manufacture dilute Cu-Cr-Zr strips. Without any heat treatments, the manufactured Cu-0.8Cr-0.06Zr alloy exhibits excellent properties, with a tensile strength of 554.9 MPa and an electrical conductivity of 80.3 % IACS. The substantial grain refinement, dynamic precipitation, and dislocation multiplication during this process can be the reasons for the enhanced mechanical and electrical properties. Consequently, no further aging treatment is required.

Continuous extrusion technology is highly suitable for producing fine-grained magnesium (Mg) alloy sheets due to its capability to accommodate large plastic deformation without repeated heating. In this study, fine-grained AZ31 Mg alloy strips with excellent ductility were successfully fabricated using continuous extrusion extending forming (CEEF). The recrystallization behavior and texture evolution during the CEEF process were systematically investigated through microstructural characterization and finite element simulations. The results revealed that the average grain size increased with the width-to-thickness ratio. At a width-to-thickness ratio of 1.89, the average grain size was refined to 2.7 mu m. The grain refinement and recrystallization during CEEF occurred in three distinct stages. Prior to the right-angle turning zone, continuous dynamic recrystallization (CDRX) was the dominant mechanism, resulting in elongated grains. In the right-angle turning zone, rotational dynamic recrystallization (RDRX), coupled with dynamic recovery, generated low-angle grain boundaries and reoriented the grains. Beyond the right-angle turning zone, limited grain growth was observed, with CDRX remaining the dominant mechanism governing the final grain size of the CEEF-processed AZ31 Mg strips. Significant textural evolution occurred during the CEEF, particularly in the pass-rolling, right-angle turning, and extrusion zones. Intense shear deformation in the right-angle turning zone activated non-basal slip, promoting the formation of a <112(-)3> fiber texture. The activation of pyramidal slip systems further contributed to the development of a rare earth (RE) texture in the extrusion zone. All products exhibited excellent ductility, with tensile elongation ranging from 22.0 % to 30.7 %. Notably, the sample with a width-to-thickness ratio of 1.89 achieved the highest elongation, while the sample with a width-to-thickness ratio of 4.57 reached the highest ultimate tensile strength of 279 MPa and an elongation of 27.5 %. These superior mechanical properties are primarily attributed to pronounced grain refinement and texture modification.

In this paper, a novel near-isometric continuous expansion extrusion was developed to fabricate copper strips. The technique was realized by modifying the deformation channels in continuous extrusion to form a C-shaped cross-section, where an accumulative strain of similar to 50 across the entire cross-section was achieved. Apart from this, the novel-designed deformation channels homogenize the strain distribution and thus facilitate the uniformity of strain rates and temperatures. Microstructure characterization and mechanical testing at the center and edge areas of the strip confirm the uniformity of the strip, demonstrating the superiority of this technique for manufacturing uniform strips. For comparison, the traditional flat strips produced by continuous extrusion were investigated, where non-uniformly distributed strain, strain rate, and temperature fields were revealed. The microstructures at the center and edge areas of the strip exhibit differences in grain size, dislocation density, and texture, resulting in different mechanical properties. Additionally, the newly designed near-isometric continuous expansion extrusion lowers the 20 % torque force, which shows great potential for extending the extrusion width-thickness ratio. Thus, compared with the traditional flat continuous extrusion and other severe plastic deformation techniques, the developed near-isometric continuous expansion extrusion shows considerable promise for manufacturing uniform metal strips.

A high strength and high electrical conductivity Cu-Cr-Zr alloy was obtained by continuous extrusion and thermomechanical treatment. Without solution treatment of the raw material, the combined process can promote the microhardness, tensile stress, and electrical conductivity to 200.4 HV0.3, 607 MPa, and 79.3 % IACS, respectively. The excellent comprehensive properties were obtained from systematically performed experiments. It was found that direct aging of as-cast or extruded alloy can not enhance the mechanical strength significantly compared with that of the extruded-rolled alloy, implying that the dislocation density plays a crucial role in the precipitation process. Cold rolling with a reduction rate of 80 % can enhance the dislocation density dramatically, promoting the precipitation process at the aging temperature of 400 degrees C. Then, the contribution of the precipitation strengthening mechanism on the total yield stress increases from 16.4 % in the extruded state to 26.4 % in the extruded-rolled-aged state. The precipitation sequence during the process was characterized as mainly meta-stable f.c.c. Cr after extrusion to stable b.c.c. Cr and Cu4Zr after thermomechanical treatment. The orientation relationship between the Cu matrix and Cu4Zr precipitates is: [011](Cu)//[100](Cu4Zr), (0 (2) over bar2)(Cu)//(040)(Cu4Zr). The investigation provides new insights into manufacturing high-performance Cu-Cr-Zr strips.

Without homogenization or special micro-alloying treatment, the tensile strength and electrical conductivity of a commercial Cu-Ni-Si alloy can achieve 813 MPa and 51.2% IACS, respectively. The excellent combination properties were achieved by regulating the thermomechanical treatment to obtain a critical status of precipitates and dislocation densities. Although a short time pre-aging process can increase the mechanical strength, the electrical conductivity was not dramatically enhanced due to the limited precipitation process. A long-time preaging process or a too-high density of dislocations is not favorable to the nucleation of new precipitates, which, instead, causes the coarsening of pre-precipitates, resulting in a limited increase in strength. A critical dislocation density can be determined to boost the nucleation sites of precipitates to simultaneously maximize the mechanical and electrical properties of Cu-Ni-Si alloys. The obtained mechanical and electrical properties can meet the requirements for very large-scale lead frames. Thus, our investigation not only provides a new route for manufacturing high-performance Cu-Ni-Si alloys but also new insights into the role of dislocations in enhancing the mechanical properties of age-hardening alloys.

Abstract The collapse of the carcass is a prominent failure mode in marine flexible pipes. This paper explores the multi-objective optimization design of the carcass layer, focusing on pivotal design variables such as the thickness of the steel strip and the height-thickness ratio of the profile. The objective functions encompass the unit length weight and critical collapse value. The optimization process integrates the BP neural network with the Non-dominated Sorting Genetic Algorithm-II (NSGA-II). Furthermore, the improved minimum distance selection method is applied to extract optimal results from the Pareto front. The insights obtained from this paper hold significant potential to contribute to engineering applications, particularly in advancing the design methodologies for carcass collapse resistance.

The manufacture of high strength, high electrical conductivity, and high ductility of Cu-Ni-Si strips in the industry is a challenging problem due to the mutually exclusive relationships among the three properties. However, the results obtained in the present study demonstrated that the trade-offs can be improved by employing a multi-pass continuous extrusion and aging process. The mechanical strength and electrical conductivity increase with the increase of extrusion number before three passes with the help of dynamically occurred recrystallization and precipitation. The yield strength, however, drops after four-pass extrusion, suggesting that a too-high strain deformation during continuous extrusion is not favorable. After aging, alloys that suffer fewer extrusion passes exhibit higher yield strengths, indicating that it is the precipitates rather than the microstructure that dominates the mechanical properties of Cu-Ni-Si alloys. Interestingly, the fracture elongation after aging for alloys experienced more pass number increases, which can be attributed to the refined grain size and reduced dislocation densities. After a two-pass continuous extrusion and aging process, the tensile strength and fracture elongation can reach 629 MPa and 16.5%, respectively, increasing approximately by 28.8% and 13.4% compared with those before aging. It is therefore significant to design an appropriate deformation process (strain) for continuous extrusion to obtain high strength, high conductivity, and high ductility Cu-Ni-Si strips.

Continuous extrusion is a very promising technique for forming Cu–Cr–Zr alloys which takes the upward continuous casted rods as raw materials. While the hot deformation behavior and constitutive equation of as-cast rods have never been reported. In the present study, the hot deformation behavior of as-cast Cu–Cr–Zr rods with columnar grains was investigated. The results showed that the flow stress at 500 °C is higher than that at 400 °C. The reason for that can be attributed to the dynamic precipitation process, which was confirmed by TEM observations. At this temperature, partial CDRX dominates the softening mechanism while at high temperatures DRV and DDRX play a critical role. The constitutive equation was then established and the deformation activation energy was determined to be 541.93 kJ/mol. The high activation energy was attributed to the large solidified columnar grains. At high strains, stable metal flows can be obtained at high strain rates and high temperatures according to the processing maps, which indicates that a high-speed deformation at a high temperature is favorable to the plastic forming of this material. This investigation thus provides valuable information on how to process the Cu–Cr–Zr rods by plastic deformation methods, for example, continuous extrusion.

A route for increasing the mechanical and electrical properties of Cu–Ni–Si alloys was proposed in the present study. Microstructure evolution and precipitation behavior were investigated in each process to tune the final properties. The results showed that dynamic recrystallization and dynamic precipitation occur partially during continuous extrusion, increasing the mechanical and electrical properties of the Cu–Ni–Si alloy. The properties were further improved by subsequent aging via different mechanisms. Aging at 400 °C or 600 °C can lead to either massive residual dislocations or early nascent precipitates in the matrix, which causes a limited increase in either electrical conductivity or mechanical strength. The properties can be compensated by eliminating dislocations and increasing the number of ripe Ni2Si precipitates at medium aging temperatures. The microstructure under these conditions, however, is not homogeneous at the edge and center areas and, the texture evolution highly depends on the aging temperature and local plastic deformation imposed. A nearly recrystallized structure possessing fine grain size and massive precipitates was achieved after an additional aging-rolling-aging process which also changes the deformed Cube 001<100> and R111<211> textures to recrystallized Brass 110<112> texture. The tensile strength and electrical conductivity then increase from 612 MPa to 763 MPa and 36.1 % IACS to 49.6 % IACS, respectively. The present results thus provide a new route and some valuable insights to manufacture high-strength and high electrical conductivity Cu–Ni–Si alloys in production.

The microstructure and impact properties of TC10 titanium alloy bar after isothermal annealing are studied by metallographic microscope, SEM and impact properties test. The results show that there were two forms of a phases in the original microstructure of TC10 titanium alloy forging bar, one was primary equiathetic a phases, the other was secondary a phases. After the alloy was annealed with isothermal temperature, the content of the equiaxed a phases in the metallographic structure decreased with the increased of temperature, and disappeared after reaching the transformation point. While the number of platelet a in the structure increased with the increased of temperature, and the size increased. The impact toughness of the alloy shows a trend that first increases and then decreases with the increase of heating temperature. When the temperature exceeded the transformation point, the impact toughness decreases significantly. With the increase of heating temperature, the fracture morphology of the alloy mainly changes from a large number of relatively deep dimples to a few relatively shallow dimples, and dissociation steps appear. After the whole investigation, it can be concluded that the best heat treatment system in this experiment was 920°C×1.5h/FC→800°C×1.5h/AC+560°C×4h/AC, and the maximum impact toughness was 49.5 J/cm2.

In the work, the cryogenic and room temperature drawing behaviors of Cu-Te alloy with a wide range of accumulative drawing true strain up to 1.1 are systematically investigated. For the first time, the storage of geometrically necessary dislocations (GND) and statically stored dislocations (SSD), occurrence of deformation twinning, as well as their respective roles in strain hardening in the drawn Cu-Te alloy at cryogenic and room temperature have been studied. The results show that the liquid nitrogen temperature drawn (LNT-D) Cu-Te alloy presents higher yield strength (YS), ultimate tensile strength than the room temperature drawn (RT-D) Cu-Te alloy. Microstructural investigation reveals that cryo-genic wire drawing of Cu-Te alloy promotes the formation of simultaneous twinning and shear bands, accompanied by the fragmentation of Cu2Te phase. The LNT-D Cu-Te alloy exhibits planar slip characteristics, while RT-D Cu-Te alloy presents wave slip charac-teristics. Compared with RT-D Cu-Te alloy, the higher YS of LNT-D Cu-Te alloy can be mainly attributed to dislocation strengthening and twinning strengthening, which account for 76.25-80.45% and 4.79-4.91% of the total YS respectively. During room temperature drawing, both GND and SSD play an important role in the hardening of Cu-Te alloy. During cryogenic temperature drawing, work hardening is predominantly through rapid multi-plication of SSDs. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

研究了上引连铸Cu-4.5Fe合金杆的热变形行为,并根据真实应力-真实应变曲线对Cu-4.5Fe合金热变形本构方程进行了推导和修正.结果表明,通过在不同应变下进行应力取值拟合的本构方程的精准性更高.此外,热加工图在不同应变条件下也不同,表明材料的热塑性与真实应变也直接相关.显微组织观察表明,Cu-4.5Fe合金的变形软化机制主要是受动态回复控制,其原因是Fe元素的加入使铜基体堆垛层错能增加,有利于位错的交滑移和攀移,从而促进了动态回复的发生.变形激活能的计算结果也证明了动态回复在塑性变形过程中会优先于动态再结晶发生.

6063 Al alloy clad AZ31 Mg alloy composite materials were fabricated by continuous extrusion under different heating temperatures with various billet diameters. The composite bars with the size of 5 mm were obtained. The microstructure and mechanical properties of the composite bars were analyzed by means of scanning electron microscope (SEM),optical microscope and tensile tests. The results show that grains in Mg core of the composite bars can be significantly refined by continuous extrusion. The average grain size of Mg core is 15.4 & mu;m. The tensile strength of the composite material is 141.4 MPa and the elongation is 6.6% when the billets are extruded at room temperature. The average grain size of the Mg core increases with the heating temperature. In addition, the tensile strength of the composite material slightly decreases but the elongation is improved to 10% when the billets are extruded at the heating temperature of 450 celcius. Moreover,the microstructure shows more homogeneous and more refined grains by using a larger diameter of Mg core. The average grain size is refined to 12.8 & mu;m. The results of SEM observation show that the interdiffusion occurs between Al and Mg during continuous extrusion. The largest thickness of the diffusion layer is 4.8 & mu;m. The highest hardness is observed at the middle of the interface. At the same time, the material flow of Al-Mg during continuous extrusion is simulated by Deform finite element (FE) software. The temperature and strain distributions of Al and Mg are obtained by the FE simulation, which is helpful to understanding the microstructure evolution during continuous extrusion.

TC11 titanium alloy was treated by solution and aging. The relationship between microstructure and impact property of the alloy after different treatments was studied by optical microscope, XRD and impact property test. The results show that after solution treatment at 955 degrees C, the microstructure of the alloy is composed of alpha(p) phase and alpha'' phase, and the morphology of alpha(p) phase is mainly equiaxed and strip-like. After solution treatment at 1015 degrees C, the microstructure is composed of alpha' phase and alpha'' phase, and the morphology of alpha' phase is fine needle-like. After aging treatment of the alloys under two groups of solution conditions, beta(T) appears in the microstructure, and alpha(s) phase is precipitated. The maximum impact toughness of the alloy is 22 J/cm(2) after solution treatment at 955 degrees C. After aging treatment, the impact toughness of the two groups of alloys decreases with the increase in aging temperature. When the solution temperature is 955 degrees C, the fracture morphology shows ductile fracture characteristics. After aging treatment, secondary cracks appear in the fracture morphology. When the solution temperature is 1015 degrees C, the fracture morphology shows brittle fracture characteristics. After aging treatment, the fracture morphology exhibits holes in addition to secondary cracks.

A novel continuous expanding extrusion process for manufacturing Cu–Cr–Zr strips was proposed in the present study. The U-shaped strips with a cross-section of 420 mm × 19 mm were successfully prepared by taking the upward continuous casted Φ 28 mm rods as raw material. Electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were employed to characterize the microstructure and precipitates, respectively, which revealed that the microstructure of the continuous extruded strip is very fine and uniform across the entire cross-section and the Cr precipitates are in a dispersed distribution in the matrix helping to improve the strength of the alloy. The average grain size is approximately 1 μm and much smaller than that of the as-cast state (in millimeters). The average micro-hardness, tensile strength, and electrical conductivity of the extruded strip are 120 HV, 328.8 MPa, and 82.6 % IACS, respectively, increasing approximately by 31.6 %, 29.3 %, and 125.5 % in comparison to these of the as-cast state. In addition, the fracture elongation can maintain a very high level (average value ∼28.9 %). The strengthening mechanisms were then quantitatively calculated, which showed that grain boundary strengthening, precipitation strengthening, and dislocation strengthening take comparable contributions. Thus, our investigations provide new insights into manufacturing high-performance Cu–Cr–Zr strips.

The purpose of this study is to investigate two new heat treatment processes on the mechanical properties of TC10 titanium alloy. By changing the β annealing temperature, the variation in microstructure and mechanical properties of TC10 titanium alloy were investigated. The results showed that with the increase in β annealing temperature the microstructure type changes from an equiaxed structure to a lamellar structure. The strength of the alloy then increases firstly, followed by a decrease, while the plasticity decreases all the time. Microstructure observation revealed that the alloy is uniformly composed of α phase and β phase after the two processes. In addition, it was found that the fracture morphology of the equiaxed structure is mainly dimples, showing ductile fracture characteristics, while the fracture morphology of lamellar microstructure is mainly crystalline, showing brittle fracture characteristics. These results indicated that reasonable β annealing temperature can be set according to different requirements to obtain different types of microstructure and mechanical properties, which expands the application field of TC10 titanium alloy.